Using Fibers as Evidence Sources Types of Fiber
Using Fibers as Evidence Sources & Types of Fiber
Fibers as Evidence Fibers are everywhere Textiles are mass produced so difficult to trace a fiber to a specific source Statistics & probability are important for narrowing source Fiber evidence is valuable because it can link victims, suspects, & places together Investigators identify & compare fibers physically & chemically
Fibers as Evidence Considered class evidence Usually unable to individualize Fibers are mass-produced in huge quantities Have probative value Can be used to create connections or associations Are common trace evidence at a crime scene Along with hair, most common type of physical evidence
Fibers as Evidence More valuable as evidence when any characteristic can limit number of sources The more properties found similar between suspect & known fibers, the stronger the case One inconsistency or property that doesn’t match, negates association Investigators generally must perform many tests to identify & compare fiber evidence
Sources and Types of Fibers Fabric is made of fibers Fibers are made of twisted filaments Types of fibers and fabric: Natural Animal, vegetable, or inorganic Artificial Synthesized or created from altered natural sources
Sources and Types of Fibers Synthetic Natural Rayon Silk Nylon Acetate Acrylic Spandex Polyester Cotton Wool Mohair Cashmere
Sources and Types of Fibers are used to make Textiles Cloth or carpeting Cordage Rope, string, nets Filling materials Mattresses, pillows, upholstery Optical cables Structural materials Used in cars, tires, & airplanes
Fibers and Fabrics Fibers used to make fabric Each fabric has its own characteristics Most fabrics made by weaving fibers Also by knitting, crochet, macrame, braiding, netting, & felting Three basic weave patterns: patterns
Fibers and Fabrics In woven fabric Warp is lengthwise yarn Stronger, smoother, & tighter twist than weft Weft is crosswise yarn Warp & weft isn’t always same material or color Called a blend Warp & weft may be different diameters Gives ribbing effect
Classification of Fibers Natural fibers are classified according to their origin: • Vegetable or cellulose • Animal or protein • Mineral
Cellulose Fibers Cotton Vegetable fiber Strong, tough, flexible & moisture-absorbent Does not retain shape Rayon Chemically altered cellulose Soft, shiny & versatile Cellulose acetate Chemically altered cellulose Created compound not found in nature
Fiber Comparison Can you see the difference between cotton on the left and rayon on the right?
Protein Fibers Wool Insulating & dries quickly Animal fiber most often from sheep Other sources Goat = mohair Rabbit = angora Camel, alpaca, llama Silk Insect fiber spun by silkworm to make cocoon Insulating & reflects light
Mineral Fibers Asbestos Natural fiber Used in fire-resistant substances Rock Wool Man-made mineral fiber Used for insulation, seed pots, etc Fiberglass Man-made inorganic fiber Used for insulation, car bodies, bathroom fixtures, etc
Synthetic Fibers Made from derivatives of petroleum, coal & natural gas Nylon Most durable of man-made fibers Extremely lightweight Polyester Most widely used man-made fiber Acrylic Lightweight, soft & resilient fiber Provides warmth Spandex Extreme elastic properties
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